Seeds changed the course of plant evolution Gymnosperms evolve ~360 mya climate became drier = selection pressures? Elkensia first fossil seed plant Seeds consist of embryo & nutrients surrounded by protective coat seeds can be dispersed long distances supply of stored food 2 living seed lineages gymnosperms ( naked seed) angiosperms ( covered seed)
Before seeds, spore was only protective structure allowed long-distance dispersal but… dependent embryo still left exposed Seeds include multi-cellular endospore = food tissue Seeds can remain dormant for a long time Gymnosperms: seeds exposed on sporophylls, form cones Angiosperms: seeds enclosed inside ovary of fruit
Miniaturization of gametophyte mosses → ferns → seed plants gametophyte became microscopic Heterosporous life cycle only 2 kinds of spores form male/female gametopytes Ovules (protect female gametophyte) sporangium kept inside sporophyte ovule contains female spores Pollen (protect male gametophyte) male spores develops into pollen grain
Cycads: 300 living species earliest evidence of insect pollination Cycads and dinosaurs lived together Gnteophytes: small and super weird group source of ephedrine Ginkos: Ginkgo biloba is only species left! super common street tree Conifers: ~600 species (cones) evergreen and deciduous leaves are needles or scales
Male and female cones on same plant scales → modified leaves → sporophyll sporophyll → sporangia → spores pollen (male) and ovulate (female) cones Male cones house microsporangium microsporangium produces microspores microspores develop into pollen grains microgametophyte inside pollen grain pollen dispersed by wind male cones usually on bottom of tree
Female cones have 2 ovules per scale each ovule has megasproangium megasporangium produce megaspores megaspore develops megagametophyte with egg Pollen grain reaches ovule and germinates pollen tube grows toward megaspore sperm → pollen tube → egg seed forms, dispersed by wind
Most diverse living group of plants 14,000 genera, >250,000 species 90% of plant diversity 2 classes: Monocots and Dicots monocots = one seed leaf in embryo dicots = two seed leaf in embryo
Flower is a modified stem for reproduction with 4 types of modified leaves Sepals: leaves at base which enclose flower usually green Petals: colored leaves to attract pollinators less colored if wind pollinated Two types of fertile organs to make spores sporophylls (male and female)
Stamens: microsporophylls produce microspores that develop into pollen Anther: where microsporangia develop microspores produced microspores → pollen pollen → male gametophyte Filament: stalk that holds the anther
Carpel: megasporophyll Stigma: receives pollen sticky Style: leads from stigma to ovary where pollen tube forms Ovary: contains ovules megasporangium inside ovule produces megaspores megaspore develops into female gametophyte w/ egg after fertilization, ovary becomes ‘fruit’